The present application relates generally to switch mode power supplies, and more specifically to switch mode power converters providing improved control of in-rush current and output voltage overshoot.
In recent years, the need for switch mode power supplies or DC-to-DC converters has risen dramatically as Integrated Circuits (ICs) such as Digital Signal Processors (DSPs) and mixed signal ICs have continued to decrease in size while their power consumption has increased. Switch mode power converters are typically employed in such ICs for converting positive or negative input supply voltages to output supply voltage levels that are appropriate for powering circuitry within the IC and/or for powering circuitry externally connected to the IC. For example, a switch mode power converter may be configured for either increasing or decreasing an input supply voltage level provided to an IC.
Conventional switch mode power converters typically include at least one soft-start circuit configured to limit in-rush currents at start-up. For example, an excessive in-rush current can cause an output voltage overshoot, which can disrupt the operation of a system processor by triggering unwanted resets. Further, excessive in-rush currents can increase the maximum current through converter components and require the use of components with increased maximum current ratings, significantly increasing the overall cost of the converter. A soft-start circuit typically feeds a constant current to an external capacitor to charge the capacitor, thereby ramping supply and reference voltages within the converter and limiting in-rush currents.
One drawback of conventional switch mode power converters is that the soft-start circuits employed therewith often do not successfully limit in-rush currents for all power converter frequencies. For example, a soft-start circuit may sufficiently limit in-rush currents when the converter operates at relatively low frequencies, but the soft-start circuit may be unable to limit in-rush currents at higher converter frequencies. As a result, while output voltage overshoots caused by excessive in-rush currents may be effectively eliminated at high duty ratios and low frequencies, output voltage overshoots may persist at low duty ratios and high frequencies.
Moreover, conventional switch mode power converters typically require more than one input for programming the soft-start timing and the converter frequency selection, thereby increasing the number of pins on the IC package and increasing costs.
It would therefore be desirable to have a switch mode power converter that limits the in-rush current at start-up over a range of switching frequencies and avoids the drawbacks of the above-described conventional switch mode power converters.